1. Field of the Invention
The present invention relates to a novel and improved system for removing flash from workpieces which have been molded from such flexible materials as rubber, plastics, and the like. More particularly, the present invention relates to the use of a flexible bellows in return and/or supply conduits of a cryogen deflashing system. In its preferred form, the present invention is practiced in conjunction with a cryogen shot blast deflashing system which 1) moves workpieces to be deflashed about in a treatment chamber, 2) exposes the workpieces in the treatment chamber to a high velocity flow of cryogen gas to rapidly embrittle workpiece flash, 3) impacts workpieces in the treatment chamber with particulate media which is projected from a throwing wheel to remove embrittled flash from the workpieces, 4) recirculates cryogen gas and particulate media from and to the treatment chamber in a highly efficient manner, and 5) utilizes a recirculating flow of pressurized cryogen gas to act as a carrier for particulate media being delivered to the throwing wheel.
2. Prior Art
When articles are molded from flexible materials such as rubber, plastics and the like, the resulting articles often have thin pieces of unwanted flexible material extending therefrom called "flash" which must be removed to conform the articles to their desired final configurations. Removing flash from articles formed from flexible materials is difficult in view of the soft, elastic nature of the flexible materials. While various types of mechanical trimming operations have been proposed for use in extricating unwanted flash, these proposals have proven not to be economically feasible in a majority of applications.
In order to simplify and reduce the cost of flash removal, proposals of various types have been made for "freezing" or otherwise cooling molded articles to embrittle their thin sections of flash, whereafter one or a combination of mechanical processes have been utilized to break off, trim or otherwise remove the "frozen" or embrittled flash. Some of these proposals have utilized a two-stage process wherein workpieces to be deflashed are cooled in a first stage to effect flash embrittlement, whereafter the cooled workpieces are vibrated, tumbled or otherwise mechanically treated in a second stage to break away or otherwise remove the embrittled flash.
Two-stage treatment processes of this type are undesirable from several viewpoints. They are time consuming to carry out because cooling the workpieces and removing their flash comprise separate steps that are carried out sequentially rather than concurrently. Inasmuch as the workpieces are cooled only once and will not be cooled again at other stages during the flash removal procedure, adequate time must be devoted at the outset to providing a thorough cooling of the workpieces to assure that they are refrigerated to an extent that their flash will remain embrittled throughout the remainder of the flash removal process. Sometimes the extensive degree of refrigeration which is required at the outset of such a two-stage process results in the generation of undesirable stresses and/or the formation of cracks or other types of structural defects in the workpieces.
An equally troublesome drawback of these two-stage processes is that, if there is a relatively large quantity of flash to be removed, the degree of refrigeration provided in the initial cooling stage may not be sufficient to keep the workpieces adequately embrittled during the entire time required for deflashing. Where such is the case, when the two-stage process has drawn to a close, the workpieces have not been properly deflashed.
The use of cryogen materials such as liquid nitrogen to effect embrittlement of workpiece flash is known. As utilized herein, the term "cryogen" will be understood to refer broadly to substances which are fluids and are at temperatures of about -60.degree. F. and below.
The use of shot blast deflashing machinery in single and plural stage processes to remove cryogen-embrittled flash is known. Previous proposals for cryogen shot blast deflashing apparatus have been characterized by a number of drawbacks. Proposed apparatus typically have been of complex and expensive construction, and have exhibited less than the desired degree of reliability. Such systems as have been proposed for 1) withdrawing particulates including media and pieces of flash from treatment chambers, 2) segregating reusable media, and 3) returning the reusable media to throwing wheels have not functioned entirely satisfactorily. Apparatus embodying a number of previous proposals have encountered problems of clogged and/or "frozen" flow lines and valves. In short, most previously proposed cryogen shot blast deflashing apparatus have been quite costly to build, costly to maintain, and costly to operate; moreover, their operation has been undependable in that it has been characterized by undesirably frequent and lengthy intervals of machine "down time."
Still other drawbacks of previously proposed cryogen shot blast deflashing systems have related to the inabilities of these systems to provide for adequate adjustment of various operating parameters throughout sufficiently wide ranges of control so that a needed variety of shot blast deflashing operations can be performed. Stated in another way, previously proposed apparatus have suffered from a pronounced lack of versatility.